1. Field of the Invention
This invention relates to a method for recording an optical recording medium of phase change type.
2. Prior Art
Highlight is recently focused on optical recording media capable of recording information at a high density and erasing the recorded information for overwriting. One typical overwritable optical recording medium is phase change optical recording medium wherein a laser beam is directed to the recording layer to change its crystalline state whereupon a change in reflectance by the crystallographic change is detected for reading of the information.
The phase change optical recording media are of great interest since the medium can be overwritten by modulating the intensity of a single laser beam and the optical system of the drive unit is simple.
The recording of information on the optical recording medium of phase change type is generally accomplished as described below. First, the recording layer as deposited in amorphous state is initialized (crystallized). In the recording, a laser beam of high power (recording power) capable of heating the recording layer to a temperature higher than the melting point is applied. In the region where the recording power is applied, the recording layer is melted and thereafter quenched to form an amorphous record mark. In the erasure of the record mark, a laser beam of the power (erasing power) capable of heating the recording layer to a temperature higher than the crystallization temperature and lower than the melting temperature is applied. The record mark to which the laser beam of erasing power is applied is heated to a temperature higher than the crystallization temperature and then allowed to slowly cool to recover the crystalline state. Accordingly, in the optical recording media of the phase change type, the medium can be overwritten by modulating the intensity of a single light beam.
Optical recording media are subject to conditions such as deterioration over time of the medium or the semiconductor light emitting device, loss of sensitivity by dust deposition, and alteration of the light power. Accordingly, test writing is generally conducted before the recording of the medium in order to enable the recording under optimal conditions by correcting such conditions. In standardized optical recording media, provision of a test write area in a part of the medium is defined in the Media Format, and the method adopted therein comprises the steps of recording the test write area with the record power being altered; determining the optimal record power on the bases of the read-out signal obtained during the test write operation, and effecting the recording of the data recording area using the thus determined optimal record power.
Japanese Patent Application Kokai No. (JP-A) 124165/1996 describes need of the test write in the phase change recording medium. However, also described is the situation that the algorithm that has been used for the detection of the optimal power needs modification if they are to be used in the phase change optical medium wherein the recording conditions are determined by two or more power levels, and that the test write method is not yet established for the phase change optical recording medium. In order to obviate such problem, JP-A 124165/1996 proposes a method for determining optimal recording and erasing powers of the semiconductor light emitting device wherein the test write operations are conducted either simultaneously or independently altering the recording power and the erasing power of the semiconductor light emitting device at respectively predetermined alteration rates.
As described above, overwrite recording of a phase change optical recording medium is conducted by modulating the power between the recording power and the erasing power. The inventors of the present invention have found that the optimal recording conditions differ by the time elapsed before the overwriting operation since the previous recording. In other words, the inventors of the present invention have found that, in the overwriting of the phase change optical recording medium, the optimal recording conditions are different depending on the recording history of the medium.
JP-A 124165/1996, however, does not disclose any means for determining the optimal recording conditions in correspondence with the recording history.
An object of the present invention is to provide a method for recording a phase change optical recording medium under optimal conditions.
Such objects are attained by the present invention as described in (1) to (3), below.
(1) A method for recording an optical recording medium which has a phase change recording layer and which has a data recording area and a test write area, wherein
the test write area is recorded before the recording of the data recording area, and the recording of the test write area is conducted corresponding to the recording history of the data recording area in order to determine optimal writing and erasing conditions for the data recording area on the basis of the quality of the read-out signal of the test write area.
(2) The optical recording method according to the above (1) wherein interval between the overwriting operations of the test write area is set to be consistent with the interval between the overwriting operations of the data recording area.
(3) The optical recording method according to the above (1) or (2) wherein, in recording the unrecorded area of the data recording area, recording in the unrecorded area of the test write area is conducted before the recording of the data recording area; and upon recording of the recorded area in the data recording area, recording in the recorded area of the test write area is conducted before the recording of the data recording area.